Vehicle brake systems

ABSTRACT

The invention relates to an automatic slack adjuster for vehicle brakes including first and second screw elements having a reversible screw thread connection therebetween. The reversible screw thread effects automatic adjustment responsively to excess travel of the brake actuator piston whereby to automatically reduce the slack. To prevent over adjustment taking place due to brake deflection when applying the brakes heavily, the brake thrust is transmitted through friction surfaces which act as a clutch to prevent unwanted rotation at the screw thread connection.

United States Patent 71.9, l06F, 196D [56] References Cited UNITEDSTATES PATENTS 2,949,]73 8/1960 Peras l88/l96 D 3,244,260 4/1966 Frayer188/196 D 3,488,687 l/1970 Farr l88/71.9X 3,550,732 l2/l970 Bellerl88/l96 D Primary Examiner-Duane A. Reger Attorney-Scrivener, Parker,Scrivener and Clarke ABSTRACT: The invention relates to an automaticslack adjuster for vehicle brakes including first and second screwelements having a reversible screw thread connection therebetween. Thereversible screw thread effects automatic adjustment responsively toexcess travel of the brake actuator piston whereby to automaticallyreduce the slack. To prevent over adjustment taking place due to brakedeflection when applying the brakes heavily, the brake thrust istransmitted through friction surfaces which act as a clutch to preventunwanted rotation at the screw thread connection.

27 17 31a 29 24 1a a r m J fl 3o 14 31 1Q 2 ti 28 12 9 PAT ENTED JAN? 1I972 SHEET 1 BF 2 VEHICLE BRAKE SYSTEMS The present invention relates toan automatic adjuster for a vehicle brake system.

It is often desirable to incorporate an automatic adjuster forautomatically taking up the slack which develops as wear of the brakelining takes place, especially in the case of a disc brake which isnormally operated hydraulically but may also be operated mechanicallye.g. by the hand brake. it has already been proposed to provide anautomatic adjuster which incorporates a screw and nut with a reversiblescrew thread connection therebetween. lt is usually necessary to providea thrust bearing, such as a ball race, to permit the nut to spin freelyin one direction and to provide a one-way clutch to prevent the nutspinning in the other direction.

One feature of the present invention is to dispense with the thrustbearing.

Since the piston travel in the case of the hydraulic actuator dependsnot only upon the normal running clearance of the brake pads but alsoupon the deflection of the caliper or other brake part under the strainof the force developed when the maximum expected brake pressure isapplied, it is desirable for the automatic adjustment to be responsiveto excess piston travel needed to take up the running clearance but notto any piston travel arising due to brake deflection. Otherwise theautomatic adjuster has to be designed to provide a rather largeclearance takeup travel to avoid the risk of the brakes binding afteradjustment consequent upon heavy brake application.

Another feature of the invention is to provide an automatic adjusterwhich is responsive only to the normal piston travel to take up therunning clearance but which does not operate once a braking force isapplied.

A further feature of the invention is to provide for a clutching actionwherein thrust is applied to one of the elements of the reversible screwthread connection to urge this element into frictional engagement with amovable brake member and so prevent said element from rotating when thebrake pressure is developed.

The present invention provides an automatic adjuster for a hydraulicbrake system comprising first and second screw elements having areversible screw thread connection therebetween and associatedrespectively with opposed first and second components of a hydraulicactuator, said members being adapted to apply a thrust to respectivebrake pads or shoes when hydraulic pressure is applied to said membersurging said pads into frictional engagement with a rotary friction disc,drum or the like.

A further feature of the invention is that the hydraulic pressure iseffectively applied to one of said screw elements and, when brake slackis developed due to lining wear, said one element is axially displacedby the hydraulic pressure to cause it to rotate on the other element andso take up the slack before the next brake application. Another featureof the invention is that, when the slack is taken up, free rotation ofsaid elements relative to one another is prevented by frictional torquearising from the thrust applied by the application of hydraulicpressure.

The adjuster can be operative between one of said actuator componentsand a mechanical actuator in the other of said actuator components.

In a preferred embodiment of the invention, the brake actuator comprisesa piston and a counter'component such as another piston slidable in acommon bore with the first mentioned piston or a cylinder in which thepiston slides. The auxiliary mechanical actuator is provided in thecounter-component and the automatic adjuster is operative between thepiston and the mechanical actuator. The mechanical actuator acts on oneelement of the screw thread connection and either the other element isattached to or forms effectively part of the piston or it comprises aseparate auxiliary piston movable into abutment with the actuatorpiston. In the former case lining wear leads to the development of aclearance between the piston and the member, such as the brake pad orshoe, upon which the piston operates. When the brake is next applied thenormal running clearance, which may be provided at the screw threadconnection or elsewhere, is taken up before the piston clearance istaken up and the piston can turn on the screw thread connection toprovide automatic adjustment to take up the excessive slack. As soon aspiston clearance has been taken up, the brake applying force istransmitted from the piston to the brake pad or shoe and the frictionaltorque thereby developed prevents the piston from rotating further. Inthe case wherein an auxiliary piston is employed, lining wear leads toclearance between the actuator piston and the auxiliary piston and thehydraulic pressure acting in the auxiliary piston takes up thisclearance to effect the automatic adjustment, until the force producedby the hydraulic pressure acting on the auxiliary piston is greater thanthe spring force.

The invention is further described, by way of example, with reference tothe accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a brake actuator fitted with anautomatic adjuster in accordance with one embodiment of the invention,and

FIG. 2 is a similar view of a second embodiment.

Referring to FIG. 1 of the drawings, a hydraulic actuator for a discbrake comprises opposed pistons 10 and 11 slidable in a through bore 12in a body member 13. The piston 10 acts upon a directly operated pad 14which cooperates with one face of a disc (not shown). The piston 11 actsupon a yoke 15 (only part of which is shown) slidably mounted on thebody member 13 and acting upon another pad (also not shown) cooperablewith the other face of the disc. The disc brake may be constructed asdescribed in British Specification No. 1,075,371.

An auxiliary mechanical actuator is fitted to the piston 11 andcomprises a cam 16 joumaled in this piston for rotation about an axisperpendicular to the actuator axis. The cam 16 acts through a dolly l7and a plunger 18 upon one end of an automatic adjuster 19 whose otherend cooperates with the piston 10. The plunger 18 is slidable in a bore9 in the piston 11 and is sealed thereto by a sealing ring 8. Theadjuster comprises a nut 20 and a rod 21 having a reversible screwthread connection 22 therebetween. A reversible screw thread connectionis a connection such that axial displacement to one element can causerotation of the other element and vice versa. This property is dependentupon the pitch angle, the flank angle and the coefficient of friction ofthe screw thread connection. The nut 20 is secured in a counter bore 23in the piston 10 but can be formed integrally with this piston ifpreferred. One end of the rod 21 is in abutment with the plunger 18 butcan be formed integrally therewith if desired. A ring 24 is locked in agroove in the rod 21 adjacent the plunger 18 and has a tab 25 bent so asto extend axially into a small offset bore 26 in the piston 11. Thisprevents the rod 21 from rotating relative to the piston 11 which isitself prevented from rotating by the yoke 15. A spring 27, in the formof a stack of Belleville washers, is housed in a shallow counter bore 28in the piston 11 and acts between a bush 29 screwed into the mount ofthis counter bore and the ring 24 to hold the rod 21 against the plunger18 and thereby hold this rod captive on the piston 11.

To apply the brakes hydraulically, hydraulic fluid is supplied betweenthe pistons 10 and 11 to urge these pistons apart. The piston 10 acts byits end face 30 upon the rear face 31a of the back plate 31 of the pad14. The piston 1] acts on the other pad through the yoke 15. The normalrunning clearance is provided by axial displacement at the screw threadconnection 22 and normally the piston 10 is not separated from the pad14. When pad wear takes place the pad 14 does not move back to quite thesame position upon release of the brake so that a small clearancedevelops between the piston face 30 and the pad back plate 31 becausethe spring 27 retracts the piston 10. The next time the brake is appliedhydraulically the clearance at the screw thread connection 22 is takenup before thrust can be transmitted to the pad 14 at the piston face 30.The piston 10 is free to rotate and is caused to rotate on the screwthread as this excessive clearance is taken up. As soon as the pad abutsthe disc a thrust is transmitted at the face 30 and the frictionaltorque thereby developed prevents the piston from rotating further. Thusadjustment can only take place while excessive running clearance isbeing taken up and overadjustment is prevented from taking place uponbrake distortion arising from heavy brake application, the additionalpiston travel being permitted by compression of the spring 27.

When the brake is applied mechanically the thrust developed at the face30 prevents the piston 10 from rotating.

The embodiment of FIG. 2 is in many respects similar to the embodimentof FIG. 1 and like parts are denoted by the same reference numerals. inthis embodiment however, the nut of the screw thread connection 22 isseparated from the piston 10a and comprises an auxiliary piston slidablein a bore 23a in the piston 100. A sealing ring 31 seals the auxiliarypiston 20a to the actuator piston 10a. The mouth of the bore 23a has aconical surface 32 which can be engaged by a complementary surface 33 onthe auxiliary piston 20a when hydraulic pressure acts upon the auxiliarypiston. The bore 23a can be formed as a blind bore and a small bleedopening 34 serves to prevent buildup of pressure at the left of theauxiliary piston 20a. The embodiment of FIG. 2 operates in the samemanner as the embodiment of FIG. 1 but axial clearance is developedbetween the conical surfaces 32 and 33 on the actuator piston 10a andthe auxiliary piston 20a when lining wear takes place rather than at theend face 30a of the piston 10a and the piston 10a does not rotate whenautomatic adjustment is taking place. The piston 10a prevents the piston20a from rotating when thrust is being applied to the brake padshydraulically or mechanically.

I claim:

1. In a vehicle brake system having first and second members movablerelative to one another upon brake application: an automatic slackadjuster disposed between said members and comprising first and secondelements associated respectively with said first and second members; areversible screw thread connection between said screw elements; meansfor urging said screw elements in an axial direction relatively to oneanother responsively to excess travel between said members to cause oneof said screw elements to advance along the other of said screw elementsand thereby reduce the brake slack; means for inhibiting reverserotation of said first screw element; and means for preventing rotationof said second screw element, said first member being normallynonrotating, said reverse rotation inhibiting means comprising frictionsurfaces associated with said first screw element and said first memberand urged into abutment with one another by the brake applying thrustupon brake application whereby said relative advance of said screwelements can only take place during takeup of slack.

2. An adjuster according to claim 1 further including a hydraulicactuator comprising opposed first and second relatively movablecomponents of which the first component is associated with said firstscrew element, and an auxiliary mechanical actuator fitted to saidsecond component, said mechanical actuator acting on said second screwelement.

3. An adjuster according to claim 2 in which said second actuatorcomponent has a bore therein and a plunger slidably received in saidbore, said mechanical actuator acting upon said second screw elementthrough said plunger.

4. An adjuster according to claim 3 further comprising a spring actingbetween said second screw element and said second actuator component andurging said second screw element relatively towards said mechanicalactuator.

5. An adjuster according to claim 4 further comprising a bush screwedinto said second actuator component and a ring fixed to said secondscrew element, said spring being disposed between said brush and saidring, said second actuator component having an axially ofi'set boretherein and said ring having an axially directed tab thereon engagingaxially displaceably in said ofiset bore. l 6. An ad uster according toclarm 3 m which said mechanical actuator comprises a cam joumaled insaid second actuator component about an axis transverse to the axis ofsaid component.

7. An adjuster according to claim 1 further comprising a hydraulicactuator having first and second relatively movable actuator components,said first screw element forming a part of said first actuator componentand said second screw element being associated with said second actuatorcomponent, said friction surfaces being disposed relatively on saidfirst actuator component and on said normally nonrotating member andnormally abutting one another.

8. An adjuster according to claim 1 further comprising a hydraulicactuator having first and second actuator components of which the firstcomponent constitutes said normally nonrotating member and the secondcomponent is associated with said second screw element, and in whichsaid first screw element comprises a nut, said friction surfaces beingdisposed respectively on said first actuator component and on said nutand normally abutting one another.

9. An adjuster according to claim 8 in which said friction surfaces arefrustoconical.

10. An adjuster according to claim 8 wherein said first actuatorcomponent has a concentric bore therein and said nut is axiallydisplaceable in said concentric bore, means being provided sealing saidnut to said axial bore.

1 1. An adjuster according to claim 2 in which said hydraulic actuatorincludes a fixed body member having a through bore and in which saidactuator components comprise opposed pistons slidable in said bore.

12. An adjuster according to claim 11 for a spot-type disc brake whichincludes a yoke slidably supported on said body member and directly andindirectly operated friction pads, said first piston acting on saiddirectly operated pad, said second piston acting on said yoke and saidyoke acting on said indirectly operated pad.

1. In a vehicle brake system having first and second members movablerelative to one another upon brake application: an automatic slackadjuster disposed between said members and comprising first and secondelements associated respectively with said first and second members; areversible screw thread connection between said screw elements; meansfor urging said screw elements in an axial direction relatively to oneanother responsively to excess travel between said members to cause oneof said screw elements to advance along the other of Said screw elementsand thereby reduce the brake slack; means for inhibiting reverserotation of said first screw element; and means for preventing rotationof said second screw element, said first member being normallynonrotating, said reverse rotation inhibiting means comprising frictionsurfaces associated with said first screw element and said first memberand urged into abutment with one another by the brake applying thrustupon brake application whereby said relative advance of said screwelements can only take place during takeup of slack.
 2. An adjusteraccording to claim 1 further including a hydraulic actuator comprisingopposed first and second relatively movable components of which thefirst component is associated with said first screw element, and anauxiliary mechanical actuator fitted to said second component, saidmechanical actuator acting on said second screw element.
 3. An adjusteraccording to claim 2 in which said second actuator component has a boretherein and a plunger slidably received in said bore, said mechanicalactuator acting upon said second screw element through said plunger. 4.An adjuster according to claim 3 further comprising a spring actingbetween said second screw element and said second actuator component andurging said second screw element relatively towards said mechanicalactuator.
 5. An adjuster according to claim 4 further comprising a bushscrewed into said second actuator component and a ring fixed to saidsecond screw element, said spring being disposed between said brush andsaid ring, said second actuator component having an axially offset boretherein and said ring having an axially directed tab thereon engagingaxially displaceably in said offset bore.
 6. An adjuster according toclaim 3 in which said mechanical actuator comprises a cam journaled insaid second actuator component about an axis transverse to the axis ofsaid component.
 7. An adjuster according to claim 1 further comprising ahydraulic actuator having first and second relatively movable actuatorcomponents, said first screw element forming a part of said firstactuator component and said second screw element being associated withsaid second actuator component, said friction surfaces being disposedrelatively on said first actuator component and on said normallynonrotating member and normally abutting one another.
 8. An adjusteraccording to claim 1 further comprising a hydraulic actuator havingfirst and second actuator components of which the first componentconstitutes said normally nonrotating member and the second component isassociated with said second screw element, and in which said first screwelement comprises a nut, said friction surfaces being disposedrespectively on said first actuator component and on said nut andnormally abutting one another.
 9. An adjuster according to claim 8 inwhich said friction surfaces are frustoconical.
 10. An adjusteraccording to claim 8 wherein said first actuator component has aconcentric bore therein and said nut is axially displaceable in saidconcentric bore, means being provided sealing said nut to said axialbore.
 11. An adjuster according to claim 2 in which said hydraulicactuator includes a fixed body member having a through bore and in whichsaid actuator components comprise opposed pistons slidable in said bore.12. An adjuster according to claim 11 for a spot-type disc brake whichincludes a yoke slidably supported on said body member and directly andindirectly operated friction pads, said first piston acting on saiddirectly operated pad, said second piston acting on said yoke and saidyoke acting on said indirectly operated pad.